Our main hypothesis is that a therapeutic agent blocking the interaction between apolipoprotein E and ?-amyloid will be effective in reducing and preventing 6-amyloid (A?) related pathology of Alzheimer's disease (AD).The ?-amyloid (A?) cascade hypothesis maintains that accumulation of the A??peptide constitutes a critical event in the early pathogenesis of AD. An excess of A? assembles into toxic oligomers and subsequently into deposits in the brain's parenchyma and in walls of vessels producing cerebral amyloid angiopathy (CAA).The direct binding between A? and apolipoprotein E (apoE) has been identified as an important factor promoting the deposition of A? in the CMS and regulating its clearance across the blood-brain-barrier (BBB).The magnitude of apoE/AB interaction appears to be isoform specific, providing one explanation for the linkage between the apoE4 allele and an increased risk of sporadic AD. We have demonstrated that blocking the apoE/AB binding with a synthetic peptide - A?12-28P, that mimics the apoE binding site on A? and was modified for in vivo application, reduces the burden of parenchynal AB deposits and CAA, as well as preventing memory impairment in AD transgenic (Tg) mice (Sadowski et al. AJP, 2004;165:937;Sadowski et al., PNAS, 2006;103:18787). In contrast, anti-A? vaccination approaches prevent only parenchymal A? deposition without affecting the CAA burden. In addition, vaccination appears to increase the risk of perivascular hemorrhages which were absent in AD Tg animals treated with A?12-28P. In this grant proposal, we are planning to develop non-toxic peptidomimetic antagonists of the apoE/A? interaction which will be based on the A?12-28 sequence. The objectives are to improve therapeutic efficacy, BBB penetration, and biostability. Due to the inherent biomimetic character of peptidomimetics, their resistance to degradation, and ease of chemical modification, this strategy has been successfully employed in the past to develop a number of therapeutically promising compounds. Selected peptidomimetic compounds will be tested in AD Tg models including those expressing differing human apoE isoforms. This will be done to predict the therapeutic response in carriers of the various human apoE isoforms. To determine whether this form of therapy can lead to a reduction of already existing A? deposits we will perform in vivo imaging of A? plaques in AD Tg mice using transcranial two-photon microscopy. Although the primary goal of blocking the apoE/A? interaction is to prevent A? fibrillar assembly and deposition there are also several other potential benefits of this approach which we investigate in this application. Thus, we will determine the effect of blocking the apoE/A? interaction on A? and apoE clearance across the BBB, the equilibrium between A? oligomers and fibril formation, and intraneuronal accumulation of apoE/A? complexes. The overall goal of this proposal is to bring this novel therapeutic approach closer to clinical studies and to identify a lead peptidomimetic compound, which could be further developed for safe, long-term application in humans.